1. Field of the Invention
The present invention relates to the field of fuel injectors.
2. Prior Art
Intensifier type fuel injectors are well known in the prior art. Such injectors use a larger first piston driven by a working fluid under pressure to drive a smaller piston to pressurize fuel for injection. Piston area ratios and thus intensification ratios typically on the order of 10 to 1 allow high injection pressures with only moderate pressure working fluid. Diesel fuel is fairly compressible at the applicable pressures. By way of example, diesel fuel compresses approximately 1% per 1000 psi. With injection pressures of 30,000 psi and higher, the compression of the fuel is substantial. The energy required for compression of the fuel not used for an injection event is generally wasted by the venting of the working fluid over the larger piston of the intensifier to a low pressure reservoir. Consequently, when an engine is running at substantially less than full power, a substantial part of the energy used for compression of a full injection charge is wasted.
Also in diesel fuel injectors, it is important to obtain a sharp start and stop of injection. A slow termination of injection, such as by a slowly decreasing injection pressure, results in poor atomization, or even no real atomization at the end of injection, resulting in incomplete combustion of the fuel, and unacceptable unburned hydrocarbon emissions.